Negative electrode for search-lights, projectors, and the like.



C. BUCHWALD, P. QUEISSER AND H. VIERTEL. EEEEEEEEE Le'cnons ron sEAR'cH LIGHTS, Pno1EcToRs,ANn me une.

v APPLICATION FILED APH. l. 9|2.' RENEWED OCT. 3.191?. L32,895 Patented Muy 6, 1919.

UNITED STATESv ,PATENT OFFICE. t

CARL BU'CHWALD, OF BERLIN, PAUL QUEISSER, 0F FRIEDENAU, NEAR BERLIN, AND HERMANN VIERTEL, F LICHTENBERG, NEAR BERLIN, GERMANY, ...SSIG-NORS TO GEBRUEDER SIEMENS & C0., OF BERLIN, GERMANY, A COPARTNERSHIP OF GER- MANY.

NEGATIVE ELECTRODE FOR SEARCH-LIGHTS, IPROJ'ECTORS, AND THE LIKE.

Specication of Letters Patent.

Patented May 6, 1919.

Application led April 1, 1912, Serial No. 687,745. Renewed October 3, 1918. Serial No. 256,763.

To all whom it may concern.'

lBe it known that we, CARL BUGHWALD, PAUL QUEISSER, and HERMANN VIERTEL, citizens of the Empire of Germany, and respectivel .residing at Berlin, Friedenau, near Berlin, and Lichtenberg, near Berlin, Germany, have invented certain new and useful Improvements in Negative Electrodes for Search-Lights,5 Projectors, and the like, of which the following is a specication.

Our invention relates to negative electrodes for search-lights, projectors and the peres, t

like.

When making `very powerful lights, such as those for lighthouses, but articularly for marine search-lights, a diliiclilty is met with, for whose removal various proposals have been made. When two carbon electrodes -arev burnt by means of the electric current and currents of considerable strength are employed, e. g., 60 to 100 amperes, and particularl in large search-lights up to 200 amhe greater the strength of current is, the more diicult it is to maintain the light `perfectly steady. e

Various proposals for keeping the light steady were based on the fact that the current readily and steadily issues from a pointed negative electrode, whereas the steadiness is done away with as soon as the original shape -of the tip of the negative electrode is changed while burning.

a quarter to half an hour, the tip of the negative carbon becomes. curved in the form of the head of an explosive shell or projectile. The Imore the tip acquires a round form the more diicult it is to maintain 'a constantly steadyfarc.

As is well-known, thepositive electrode-` acquires a very highly crater-like shape, and as the current always selects the best path,

" e z'. e., the shortest path under like conditions,

the distance 'from the edge of the crater of the positive carbon to the curved end of the negative carbon is shorter than the 'axial distance between the two carbons.

The current goes from the negative carbon ously leaves the point of the negative carbon and then 4flows along the unavoidable residues of the two carbons; the arc begins to hiss and as the negative carbon has lost its point it is impossible to make the light stead again without mechanically repointlng t e negative carbon.

' Now various proposals have been made for maintaining the negative carbon with a burning point. Negative carbons have been made comprisingla core of carbon more refractory than the shell. Such carbons having more refractory shells were not satisfactory, as they had other defects and did not attain the end in view.

It has also been attempted to employ relatlvely thin carbons, and it'has been proposed to stop the smoldering of the same due to their ohmic resistance by surrounding them with a fire'proof protective casing. This method of surrounding carbons with a ireproof protective casing led, it is true, tol

inorder to make them as thin as possible; After burning a relatively short ltlme, say

this also attained its'f-purposeV to` a certain extent; but has the great defect that the copper melts and drops of copper splash on the reflector, whereb -the expensive reiiectors 1 makers 0f search-lights @11d Sel'h'lght Cal'- Again, it has been very generally attempt-f question, and' preferably over the central while the soft bons had to continue to endeavor to ind a mode of guaranteeing absolute steadiness of the light in a search-light.

For marine purposes it is absolutely necessary to illummate the objectfwhich is to be illuminated without fiickerin of the light, z'. e., without the light of te search-light fluctuating and quivering. Otherwise even the most powerful light is ynot crowned with the desired success.

Now a primary object o'f our invention is to provide improved negative electrodes by which the end in view is more nearly attained than has been the case heretofore. Essentially our inventionconsists in embedding within a large outer body carbon of usual well known construction, cores which are separately well lrnown in the art as hard never before so far as we are aware been used together within the larger outer body of refractory carbon which is relatively a poor conductor as compared to the hard core- 'and very much more` refractory than the Soft core. In this combination of el'ements the current will flow principally through the hard core by reason of its capacity for increasing the conductivity of the arc will prevent such arc jumping from the hard?core to the hard outershell of the main body carbon.

The apparatuses in question `must in by far the majority `of cases be provided with horizontal carbon electrodes. r Owing to the air beingl heated itrises, of course, with considerable buoyancy. Now as soon as the' negative carbon has lost its slender and sharp point, as mentioned above, the buoyancy ofthe hot air causes the seatof the arc at the negative carbon to be shifted from the .tip upward. As soon as this has taken place to any` considerable extent owing to the risingr current of air, the danger ofthe arc settling at the outer shell ofthe two carbons increases, and at the same moment the arc b'ecomesuns'teady and ickers and hisses disagreeably.

Therefore, we provide near the core in core which is intended to fix the arc, a mass which supplies to the'arc 'a suiicent quantityiof rthose substances which increase its conductivity. We do thi 's by arranging over the central core which may be copperplated or provided with any other electrically con# ducting eoatlng a channel which we ill with substances which solely increase-the conductivity of the arc.

Several illustrative embodiments of our invention are represented by way of example in the accompanying drawing, wherein Flgures 1 to 6 are diagrammatic cross-Secand soft cores but which cores have good conducting core `tions showing various forms of our improved carbons each provided with a hard core and an auxiliary, arc-feeding core according to our invention. Fig. 7 represents a longitudinal section of Fig. 1.

Referring to the drawing, we may either `employ an arc-feeding core b over the central core a as shown in Fig. 1, or we may use a iattened central core a1 and lill the resulting chamber with a iattened core b, composed of the arc-feeding mass, as shown4 in Fig. 9 wherebyy one composite core al, b1 of circular section is obtained.

In the form shown in Fig. 3 we provide in the upper part of the central core a a core b of circular section composed of the arcfeeding mass.

As Fig. 4: shows, instead of using a round central core we may use a flattened oval c'entral core a2, its ulpper part being substituted with a core b2 composed of the arc-feeding mass, whereby a ,composite core a2, b2' of oval sectionis obtained.

Furthermore, we may arrange in the negative electrode a carbon tube a3 which is cop perplated or has been made a godd electrical conductor in another manner, and fill this tube with a core b composed of the substances in' question which make the arc a good electricalconductor, as shown in Fig. 5.

4Insearch-lights in which the axis ofthe electrode is horizontal, as shown in Fig. 6, we prefer, however, for the axis of the carbon tube a3 to be located above the axis of the electrode in order thus to take account of the existing circumstances.

In all forms embodying our invention we use a combination `of va solid, good electrically conducting core which is as highly refractory as possible, with a core which sufficiently xes the arc.

Thus the essence of the invention is the arrangement, in negative electrodes for search-lights, of a combination core which comprises, on the one hand, ahard core which is a good electrical conductor in itself or is made a good electrical conductor by electroplating, for maintaining as good conductivity of. the entire carbon as possible, and, on 'the other hand, a core which feeds the arc and tends to preventthe arc moving away from the point.

We claim l. A negative electrode `for searchlights, containing a separately fired hardcore constituting a good current conductor and consisting of tar and carbon, and a soft c'ore consisting essentially of carbon and water glass and whose ingredients increase the conductivity of the arc.

`2. A negative electrode for searchlights containing a hard core which is a good coni `5 comprising an outer electrode body, a hard sisting of material which increases the oon-` In testimony whereof We have signed oui` ductivity of the arc, said soft core being connames to this specication in thepresence of centrically arranged Withinaid hard core.- two witnesses.

3. A negative electrode for searchlighfs, CARL BUCHWALD good conducting core of relatively large' cross-sectional area, and a soft; core of relatively small cross-sectional area composed of Witnesses: material which increases the conductivity of HENRY HASPER, 10 the are. Y WOLDEMAR HAUPT. 

